[OpenSCAD] CGAL error depends on order of unioning

nop head nop.head at gmail.com
Tue Jul 23 05:36:13 EDT 2019

It probably isn't a bug. It is quite possible to have three objects such
that unioning two of them gives a non-manifold result but unioning them in
another order doesn't. For example consider two cubes sharing one edge and
a third that overlaps that edge. If you do the union one, two, three you
will get an error but one, three, two will work and so will any other order
because the intermediate results are all manifold.

On Tue, 23 Jul 2019 at 10:08, Shaporev, Timur <tim at auriga.com> wrote:

> While working on https://www.thingiverse.com/thing:3762730 I faced
> strange effect: script produce
> ERROR: CGAL error in CGALUtils::applyBinaryOperator union: CGAL ERROR:
> assertion violation! Expr: itl != it->second.end() File:
> /mxe/usr/x86_64-w64-mingw32.static.posix/include/CGAL/Nef_3/SNC_external_structure.h
> Line: 1152
> on F6 but some change in order of unioning yields expected result.
> I am attaching an archive with both faulty and good versions of scripts.
> (The scripts render long enough: more than 20 minutes to preview the first
> script on my PC and 6 more minutes to render, yet more for the second
> script.)
> If this is new issue I'd appreciate advice on how to (get a ticket number)
> register it.
> Thank you,
> Tim
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